Although this invention is applicable to the machining of the inside surface of various types of closed hollow casings or housings, it has been found particularly useful in the environment of the machining of the two halves of the hollow casing or housing of a turbomachine, e.g. a compressor, with the two halves positioned to form a closed hollow casing or housing. Therefore, without limiting the applicability of the invention to "the machining of the inside surface of the closed hollow casing for a compressor", the invention will be described in such environment.
In the production of the casing or housing for turbomachines, e.g. large compressors in the 3, 4 and 5M ranges, it is necessary to machine the inside diameters, contoured areas, shoulders, return bend areas, etc. In the past, the machining process has been a tedious and time consuming task for a number of reasons. In the prior method of machining, only one half of the casing was machined at a time and then the other half of the casing was machined. The problem that occurred because of this procedure was that when the two halves were combined to form the overall casing, the machined areas did not always align and mate between the two halves.
In the machining of one of the halves of the casing, a boring bar was rotatably supported in the half casing, a boring head was attached to the boring bar and a single cutting bit was bolted to the boring head. When a groove or a deeper cut was to be machined into the inside surface, the boring bar was rotated and the cutting bit cut a groove. The boring bar was then stopped, the screws holding the cutting bit were loosened, a dial indicator would be placed up against the cutting bit and boring head, the cutting bit would be extended radially an amount determined by the proper reading on the dial indicator, the screws holding the cutting bit were tightened and the boring bar would then be rotated and the process would be repeated until the proper depth of the groove was achieved. If the groove or channel to be machined was wider than the cutting bit, then the boring bar would be moved axially and the cutting process would be repeated. It will be greatly appreciated that the problem with this procedure is the great amount of time required to machine the inside surface of each half of the casing.
An even larger problem occurred when it was necessary to machine a return bend in the surface with a return bend being a groove in the shape of a half cylinder. Then it was not only necessary to extend the cutting bit radially after each cut but it was also necessary to axially move the boring bar after each cut in order to obtain the arc shape at the bottom of the groove. It was not possible to plunge-cut the return bend in the inside surface of the half casing.
The present invention overcomes these problems by providing apparatus which machines the two halves of the casing in one operation while the two halves are positioned and mated together to form the complete casing thereby providing machined areas in the inside surface of the two halves which machined areas are symmetrical and in line. The present invention also provides the capability of plunge-cut machining without stopping the machining process. The machining process can be started and run through completion without stopping to change the position of the cutter tool or insert since the position of the cutter tool or insert is moved to various predetermined positions while it is being rotated within the casing. The present invention allows the machining process to be completed in a much shorter time than with the prior art because the positioning of the cutter tool or insert is changed without stopping the process and because two cutter tools or inserts are provided rather than just one. The present invention machines return bends on the inside surface of the casing without stopping the machining process. The machining is much more precise and accurate.